This invention relates to tube benders and more particularly to tube benders capable of effecting bends in tubing of differing diameters.
For many years, electricians have been using tube benders to effect bends in electrical conduit. Similarly plumbers and other craftsmen have used tube benders to produce bends in tubes for a variety of applications. A typical tube bender has a form wheel which is arcuate in cross section both in an imaginary plane including an axis about which a tubular work piece is bent and in cross section in a plane orthogonal to the axial plane. The form wheel is secured to a handle while a form shoe having complemental surfaces is secured to a second handle and the handles are pivotally connected together. A hook arrangement is provided to retain a work piece in appropriate orientation with a groove in the wheel as a bending operation is effected by relatively rotating the handles such that the form shoe orbits around the wheel groove.
There have been proposals for form wheels with sets of grooves which have different of arcuate surfaces in axial cross section. A shortcoming of these has been that the radii of groove curvature about the wheel axis is a constant such that the radii for smaller tube bends are excessively large. Indeed because the prior hook arrangements are uniformly spaced from the wheel axis the radii of bends in smaller diameter tubes are actually greater than those of larger diameter tubes. Moreover, when bends have been made to an extent measured by a tool mounted protractor, the true angle of a bend has only been accurate for one tube diameter. Thus if a tool gives an accurate indication of a 90 degree bend in a large diameter tool, bends in smaller tubes, producing the same measurement will be less than 90 degrees.
With tube benders it is desirable to have handles of different lengths so that a bending operation can be effected by an operator gripping the handles without either grip being interfered with by the other handle. There have been tube benders in which this is accomplished by having handles which are offset and of different length but the longer handle has been connected to the form wheel with a result that the forming leverage has not been maximized.
Accordingly, it would be desirable to provide a tool for bending tubing to a range of bend radii especially one which is especially suited for bending copper tubing of a range of diameters.
With the bender of the present invention, a pair of handles of differing length are pivotally connected together by a link. A form wheel is secured to the shorter of the handles. The form wheel has three grooves of differing sizes. That is there is a) a large groove which of the three has the largest radius of curvature in both an axial plane and a plane normal to the axis, b) a second groove of intermediate size with a radius in the axial plane that is shorter than the large groove and c) a smaller third groove. Similarly the radii of curvature of the three grooves are large, medium and small. The three sized grooves are provided so that each groove is designed to accommodate tubing of a standard size such as xc2xd, xe2x85x9c, and xc2xc inch diameters.
A form shoe is secured to the other and the longer of the handles. The form shoe has three sizes of grooves that are arcuately curved in the same axial plane of cross section as the wheel grooves. In planes normal to the wheel axis the shoe grooves are straight. The shoe grooves are complemental in axial cross section with the wheel grooves and radially aligned such that as the handles are rotated about the pivot, a work piece is engaged and substantially surrounded by the complemental pair of the grooves of the appropriate and matched size.
A work piece holder is provided to retain a work piece in an associated wheel groove and resist forces applied by the shoe as the shoe orbits the wheel. Unlike prior art holders with the holder of the tool of the present invention that part of the hook surface which resists binding forces applied to a smaller tube is closer to the axis of the form wheel then those parts which resist bending forces of larger diameter tubes. While a hook with stepped tube engagement parts will produce small, medium and large radii bends, the preferred and disclosed hook is shiftable to a selected one of three locations, each spaced from the wheel axis in an amount appropriate for bending of a tube in an associated one of the wheel grooves. The holder and the wheel handle have a coacting tongue and groove arrangement for registering the holder selectively and one at a time in a selected and appropriate one of its three positions. A stepped and preferred hook arrangement results in consistent bonds of appropriate radii when measured on a tube mounted protractor.
Accordingly the objects of this invention are to provide a novel and improved tube bender suitable for use with tubing of differing diameters and a process of bending tubing.